Techniques serving as a foundation of a manufacturing industry in Japan includes a molding technique. The molding technique includes a method for an injection-molding, a method for a compression-molding, and a method for an extrusion-molding for example. In these methods, the method for the injection-molding is a method for injecting a melt resin in an injection mold, followed by cooling and subsequently solidifying the melt resin to obtain a molded article.
Recently, a demand for an air purifier has been increased in accordance with a degradation of an air environment. The air purifier has a molded article in a form of a filter for catching suspended substances in an atmosphere, the molded article corresponding to a filter part. The molded article in the form of the filter is obtained by the injection mold having a cavity space of a fine mesh structure. A melt resin is needed to be injected in the cavity space having the fine mesh structure in the injection mold to obtain the molded article in the form of the filter. However, the fine mesh structure of the cavity space is likely to result in a remaining of a gas arising from the melt resin in the cavity space.
In this regard, Patent document 1 discloses an injection mold in which a nested part composed of a vent part surrounds a cavity space. In the injection mold of the Patent document 1, a gas in the cavity space is discharged through the vent part surrounding the cavity space. Specifically, when a melt resin is injected into the cavity space under a condition of a vacuum, the gas in the cavity space is discharged through the vent part to a vent passage which is on a condition of a reduced pressure.